The wear of alloy workpieces is largely affected by the contact stress or impact stress on the surface. Surface wear under stress depends on the interaction characteristics of dislocation flow and contact surface. For cobalt-based alloys, this feature is related to the lower stacking fault energy of the matrix and the transformation of the matrix structure from face-centered cubic to hexagonal close-packed crystal structure under the effect of stress or temperature. Metals with hexagonal close-packed crystal structure Material, wear resistance is better. In addition, the content, morphology and distribution of the second phase of the alloy such as carbides also have an impact on the wear resistance. Because the alloy carbides of chromium, tungsten and molybdenum are distributed in the cobalt-rich matrix and part of the chromium, tungsten and molybdenum atoms are solid-dissolved in the matrix, the alloy is strengthened, thereby improving wear resistance. In cast cobalt-based alloys, the size of carbide particles is related to the cooling rate. Faster cooling means finer carbide particles. In sand casting, the hardness of the alloy is low, and the carbide particles are also coarser. In this state, the abrasive wear resistance of the alloy is significantly better than that of graphite casting (fine carbide particles), and the adhesive wear resistance of both There is no obvious difference, indicating that coarse carbides are beneficial to improve the ability of abrasive wear resistance.
The size and distribution of carbide particles and grain size in cobalt-based alloys are very sensitive to the casting process. In order to achieve the required durability and thermal fatigue performance of cast cobalt-based alloy parts, the casting process parameters must be controlled. Cobalt-based alloys need heat treatment, mainly to control the precipitation of carbides. For cast cobalt-based alloys, first perform high-temperature solid solution treatment, usually at a temperature of about 1150°C, so that all primary carbides, including some MC-type carbides, are dissolved into solid solution; then, they are aged at 870-980°C. Make carbides precipitate again.
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